1. Field of the Invention
The present invention relates to an apparatus and method for transmitting/receiving data in a wireless local area network (WLAN) mesh communication system. More particularly, the present invention relates to an apparatus and method for reliably transmitting/receiving broadcast/multicast data in a WLAN mesh communication system using a multi-channel.
2. Description of the Related Art
In general, a wireless LAN is different from a conventional wired local area network (wired LAN), in that a wireless LAN (WLAN) uses a wireless medium for data transmission. As such, a wireless LAN does not need a connection cable which is necessary in the conventional wired LAN. The current WLAN uses radio frequencies in order to transmit/receive data so that the WLAN has been highlighted as a network capable of extending or replacing the conventional wired LAN.
The WLAN is based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. Particularly, among the IEEE 802.11 standard, the standardization of IEEE 802.11s which does not require a cable connection between access points (APs) is actively progressing. A WLAN mesh communication system, which is a WLAN communication system defined in the IEEE 802.11s standard, defines even wireless connection between networks, thereby facilitating the installation of a network even in an area in which it is difficult to install the conventional WLAN.
The WLAN mesh communication system includes a plurality of nodes for transmitting/receiving data. The nodes include a plurality of stations (STAs), a plurality of mesh points (MPs), and a plurality of mesh access points (MAPs). Herein, the MP supports a mesh service, and the MAP refers to a specific MP and provides an AP service for managing the STAs as well as the mesh service.
The structure of the WLAN mesh communication system will now be described with reference to FIG. 1.
FIG. 1 is a view illustrating the structure of a general WLAN mesh communication system.
The WLAN mesh communication system includes a plurality of nodes 100, 110, 120, 130, 140, and 150. Herein, each node 100, 110, 120, 130, 140, or 150 may be an STA, an MP, or an MAP, as described above. However, for example, an STA may exclusively make communication with an MAP. The node 150 and the node 100 may correspond to the STA and MAP, respectively.
That is, the STA 150 can exclusively receive the signals from the MAP 100.
Herein, it is assumed that one transmission node 110 transmits data to predetermined reception nodes 120, 130, 140, and 150. To this end, the transmission node 110 transmits data to the reception nodes 120, 130, 140, and 150 in a multicast scheme. Hereinafter, the operations of the transmission node and reception nodes for transmitting/receiving data based on the multicast scheme will be described with reference to FIG. 2.
FIG. 2 is a view schematically illustrating a data transmission/reception flow in a general WLAN mesh communication system.
That is, FIG. 2 schematically shows data transmission/reception operations of the transmission node and reception nodes and control signals between the transmission node and reception nodes based on time. Herein, the control signals refer to information transmitted/received between the transmission node and reception nodes in order to transmit/receive data.
Before transmitting data to predetermined reception nodes, the transmission node broadcasts an RTS (Request To Send), checking if the predetermined reception nodes are ready to receive data, to nodes surrounding the transmission node. Herein, the RTS, a CTS (Clear to Send), and an ACK (Acknowledge) are transmitted to achieve reliable data transmission in a broadcast/multicast scheme.
When each predetermined reception node, which is to receive data from the transmission node, receives the RTS, the predetermined reception node determines if it is ready to receive data. When it is determined that the predetermined reception terminal is ready to receive data, the predetermined reception terminal transmits a CTS signal to the transmission node, thereby notifying the transmission node that the predetermined reception terminal is ready to receive data.
Herein, it is assumed that the transmission node is currently transmitting data to reception nodes, and the transmission node desires to transmit data to “n” reception nodes. In the case of using the multicast scheme, the transmission node uses a specific multicast address in order to identify reception nodes. Referring to FIG. 1, for example, a broadcast address is set to “1010” so as to be used for identifying two specific nodes 130 and 140. Also, in the case of using the broadcast scheme, in order to identify reception nodes, the broadcast address is set to “−1” (all bit values are marked with “1” when it is expressed as a binary number), thereby identifying all nodes surrounding the transmission node.
In order to transmit data after transmitting the RTS, the transmission node must receive all “n” CTS signals from the “n” reception nodes. After having received all the “n” CTS signals, the transmission node transmits data to the reception nodes.
In contrast, if the transmission node has not received all the “n” CTS signals, the transmission node re-transmits the RTSs to the reception nodes, and then transmits the data only when having received all the “n” CTS signals.
After having received the data from the transmission node, each reception node transmits an ACK message for representing data reception completion to the transmission node (i.e. MAP), thereby notifying the transmission node that the corresponding reception node has received the data. When the transmission node has received “n” ACK messages because there are “n” reception nodes, data transmission/reception between the transmission node and the reception nodes have been completed.
Meanwhile, in order to transmit data to the reception nodes in a multicast scheme, the transmission node waits for CTS signals after transmitting an RTS. In this case, as the number of reception nodes, to which the transmission node desires to transmit data, increases, that is, as the value of “n” becomes larger, the number of CTS signals to be received by the transmission node increases. Therefore, it is necessary for the transmission node to receive a plurality of CTS signals in order to transmit data to a plurality of reception nodes, thereby wasting resources for data transmission, such as bandwidths, power, and the like.
Meanwhile, when a reception node is not ready to receive data, the reception node cannot send a CTS signal to the transmission node. Therefore, if any one of reception nodes to receive data from the transmission node is not ready to receive data, the transmission node repeatedly performs the RTS transmission procedure. Accordingly, when the transmission node does not receive the CTS signal in the WLAN mesh communication system, the resources are more greatly wasted.
Accordingly, there is a need for an improved apparatus and method for transmitting/receiving data in a wireless local area network mesh communication system.